Syphilis cases have reportedly reached the highest level in England since 1949 following a rise in unsafe sex as fears about HIV have faded, new figures indicate.

According to the Telegraph, the data shows the number of diagnoses doubled in five years, with most cases occurring in gay and bisexual men.

It follows warnings from health officials risky sexual behaviors are fueling the rise, including the use of "hookup" apps like Grindr, the Telegraph reported.

The figures from Public Health England show 5,920 syphilis diagnoses in 2016 – a rise of 12 percent in one year, and a near doubling from 3,001 cases in 2012, the Telegraph reported.

In the United States, the Centers for Disease Control and Prevention said in an October 2016 report the biggest increases in sexually transmitted disease cases from 2014 to 2015 occurred in syphilis – at 19 percent – followed by gonorrhea, at 12.8 percent and chlamydia, at 5.9 percent.

"Chlamydia, gonorrhea, and syphilis are the three most commonly reported conditions in the nation and have reached a record high level," the CDC said at the time.

Dr. Michael Brady, medical director at sexual health charity the Terrence Higgins Trust in England, told the Telegraph rates of syphilis infections were "unacceptably high" and said cuts to public health budgets were fueling a "sexual health crisis."